Method of etching materials with electron beam and laser energy

ABSTRACT

We disclose a method of electron-beam induced of etching the surface of a specimen in a charged-particle beam instrument, where the charged-particle beam instrument has first and second laser beams, an electron beam, and a gas-injection system for applying etchant gas to the surface. Etching is accomplished by applying a photolytic pulse from the first laser to the surface; applying a pyrolytic pulse from the second laser to the surface; and, applying an etchant gas to the surface at least during the pyrolytic pulse. Two or more alternating pyrolytic laser pulses and photolytic laser pulses may be applied to the surface. The stage supporting the specimen may be tilted relative to the axis of the electron beam before applying the electron beam to the surface of the specimen. The electron beam is applied to the surface of the specimen during the time the etchant gas is present at the surface.

CLAIM FOR PRIORITY

This application claims the priority of U.S. Provisional Application Ser. No. 61/151,687, filed Feb. 11, 2009, which provisional application is incorporated by reference into the present application.

CO-PENDING APPLICATIONS

This application is related to co-pending applications Ser. No. 12/211,638, titled “Methods for electron-beam induced deposition of material inside charged-particle microscopes,” filed Sep. 16, 2008, and Ser. No. 12/399,579, titled “Method and apparatus for precursor delivery system of irradiation beam instruments,” filed Mar. 6, 2009.

BACKGROUND

1. Technical Field

This disclosure relates to systems and methods for the inspection and modification of surfaces and microscopic and nanostructures in charged-particle beam instruments; in particular for the inspection and edit of integrated circuits, semiconductor wafers and photolithographic masks and optical beam analytical methods. Examples of charged-particle beam instruments are focused ion-beam microscopes (FIB's) and scanning electron microscopes (SEM's). Typical modern FIB's include an ion beam, an electron beam and ports for additional instruments, such as gas injectors, manipulators and x-ray analyzers.

2. Background Art

Certain techniques for use of an electron beam in charged-particle beam instruments for etching or depositing material are known. Some techniques are described in U.S. Pat. No. 6,753,538 B to Musil, et al., which patent is incorporated by reference into this application, but which is not admitted to be prior art by inclusion in this Background section. The electron-beam induced etch method is frequently used for editing the microscopic and nanostructures receiving the most attention in industry and research. The simultaneous use of optical energy together with the electron beam aids navigation to the area of interest, the monitoring of the process, and enhances the rate or selectivity of the etch process. As was shown lately in the art, the deposition and etch processes can be significantly improved by changing the temperature of the specimen surface being processed.

DRAWINGS

FIG. 1 shows a schematic layout of a stage in a charged-particle beam instrument, where the instrument has an electron beam, one or more lasers, a gas-injection system and a secondary electron detector.

FIG. 2 shows a schematic layout of the same system with a two lasers for creating both photolytic and pyrolytic effects at the surface of a specimen while there is a flow of etchant gas onto the surface.

FIG. 3 is a graph of pulses of laser energy, energetic electrons, and etchant gas against time.

FIG. 4 is a flow chart of embodiments of the methods for etching disclosed here.

DESCRIPTION

FIGS. 1 and 2 show schematic layouts of a stage (105) in a charged-particle beam instrument, where the instrument has an electron beam (120), one or more lasers (130, 140), a gas-injection system (150) and a secondary electron detector (170). In FIG. 2, there is a flow of etchant gas (180) onto an area of interest (110) located at a specimen surface (100). As is known in the art, reactant compounds suitable for etching, are chemistries based on fluorine, chlorine, bromine, or oxygen. A suitable gas-injection system (150) is the OmniGIS multiple gas-injection system, manufactured by Omniprobe, Inc., of Dallas, Tex.

FIG. 2 shows the application of a pyrolytic laser beam (130) and a photolytic laser beam (140) to the surface (100) at the area of interest (110). In this application “pyrolytic” refers to laser energy substantially in the wavelength range of about 400 nm to about 3000 nm (the visual and infrared region) that is applied to heat the area of interest, thus accelerating the desired chemical reactions. In this application, “photolytic” refers to laser energy substantially in the wavelength range of about 190 nm to about 400 nm, the ultraviolet region.

FIG. 3 is a time versus amplitude graph, not to scale, to schematically illustrate methods for applying a photolytic laser pulse (240), a pyrolytic laser pulse (230), along with etchant-gas flow periods (220), and electron beam (120) application periods (210). Conventional heating (200) of the stage (105) supporting the specimen surface (100) may also be applied.

Typically, the surface is imaged by the electron beam (120) scan of the charged-particle beam instrument and the area of interest (110) on the specimen surface (100) is located by known means. Existing contamination on the surface (100) may be cleaned by application of a photolytic laser pulse (240).

In the preferred embodiment, our method of etching the surface (100) of a specimen in a charged-particle beam instrument comprises applying a photolytic pulse (240) from a second laser (140) to the area of interest (110), applying a pyrolytic pulse (230) from a first laser (130) to the surface (100) to heat the surface (100); applying an etchant gas (180) to the surface (100) at least during the pyrolytic pulse (230). In other embodiments, there can be two or more alternating pyrolytic laser pulses (230) and photolytic laser pulses (240), and optional additional pulses (245) as shown in FIG. 3. Typically, the electron beam (120) would be applied to the surface (100) in a pattern to cause the emission of secondary electrons (115) that induce the desired chemical reactions in the area of interest (110) on the surface (100).

At any point after application of the etchant gas (180), the surface (100) may be imaged to determine if the etching of the surface (100) is completed; and, if the etching of the surface (100) is not completed, then the application of the pyrolytic laser pulse (230), the photolytic laser pulse (240) and the application of the etchant gas (180) may be repeated. The photolytic laser pulse (240) will increase the rate of etching by removing contamination products from the area of interest (110) and help prevent the condensation of these products at the surface (100). It is advisable to turn off the flow of etchant gas (180) and the electron beam (120) during the photolytic pulse (240) to avoid interactions between them that could interfere with the etching process.

We have found it usually desirable to tilt the stage (105) supporting the surface (100) relative to the axis of the electron beam (120) before applying the electron beam (120) to the surface of the specimen. As shown in the configuration depicted in FIG. 2, the tilt of the stage (105 helps to improve the pyrolytic laser beam (230) focus on the area of interest (110) of the surface (100); that is, the pyrolytic laser beam (230) can be made substantially perpendicular to a particular area of interest (110) on the surface (100). The stage (105) tilt leads to improved etching reaction rate because of the favorable distribution of secondary electrons (115) originated as a result of the interaction of primary electrons delivered by the electron beam (120) and the specimen surface (100), and also due to less re-deposition of contaminants. In any case, it is preferable to adjust the energy of the electron beam (120) to maximize secondary electron (115) emission from the surface (100).

FIG. 4 is a flow chart depicting generally the steps of the foregoing methods. At step 400, the area of interest (110) on the surface (100) is located. At step 405, the stage (105) is optionally tilted. Usually, at step 410 a photolytic laser pulse (240) is applied to clean the surface (100). At steps 415 and 420, the electron beam (120) is turned on and the gas-injection system (150) begins the flow of etchant gas (180) onto the surface (100).

Step 425 represents the application of the pyrolytic laser pulse (230) and the electron beam (120). At step 430, the flow of gas (180) is stopped, and the photolytic laser pulse (240) is applied at step 435. At step 440, the surface (100) may be imaged to determine the progress of the etching process. At step 445, if the cleaning-heating-gas-electron beam cycle must be repeated to complete etching, the process returns to step 410; else, the etching process is complete at step 450.

None of the description in this application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope; the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke paragraph six of 35 U.S.C. Section 112 unless the exact words “means for” are used, followed by a gerund. The claims as filed are intended to be as comprehensive as possible, and no subject matter is intentionally relinquished, dedicated, or abandoned. 

1. A method of etching the surface of a specimen in a charged-particle beam instrument, where the charged-particle beam instrument has first and second laser beams, an electron beam, and a gas-injection system for applying etchant gas to the surface, the method comprising: applying a photolytic pulse from the first laser to the surface; applying a pyrolytic pulse from the second laser to the surface; and, applying an etchant gas to the surface at least during the pyrolytic pulse.
 2. The method of claim 1, comprising two or more alternating pyrolytic laser pulses and photolytic laser pulses.
 3. The method of claim 1, further comprising: imaging the surface after the application of the etchant gas to determine if the etching of the surface is completed; and, if the etching of the surface is not completed, then, repeating the application of the photolytic laser pulse, the pyrolytic laser pulse and the application of the etchant gas.
 4. The method of claim 1, further comprising: applying the electron beam to the surface of the specimen during the application of the etchant gas.
 5. The method of claim 4, where the charged-particle beam instrument further comprises a stage supporting the specimen, the method further comprising: tilting the stage supporting the specimen relative to the axis of the electron beam before applying the electron beam to the surface of the specimen; and, applying the electron beam to the surface of the specimen during the time the etchant gas is present at the surface.
 6. The method of claim 5, where the energy of the electron beam is selected to substantially maximize secondary electron emission from the surface.
 7. The method of claim 1, where the charged-particle beam instrument further comprises a stage supporting the specimen, the method further comprising: applying the electron beam to the surface of the specimen both during the time the etchant gas is present at the surface and during the time the pyrolytic laser beam is applied to the surface.
 8. The method of claim 7, further comprising: tilting the stage supporting the specimen relative to the axis of the electron beam before applying the electron beam to the surface of the specimen; and, applying the electron beam to the surface of the specimen during the time the etchant gas is present at the surface.
 9. The method of claim 8, where the energy of the electron beam is selected to substantially maximize secondary electron emission from the surface.
 10. A method of etching the surface of a specimen in a charged-particle beam instrument, where the charged-particle beam instrument has a stage supporting the specimen, an electron beam, a pyrolytic laser beam, and a gas-injection system for applying etchant gas to the surface, the method comprising: tilting the stage supporting the specimen relative to the axis of the electron beam; applying the etchant gas to the surface; and, applying the pyrolytic laser beam to the surface; and, applying the electron beam to the surface of the specimen during the time the etchant gas is present at the surface and during the time the pyrolytic laser beam is applied to the surface.
 11. The method of claim 10, where the energy of the electron beam is selected to substantially maximize secondary electron emission from the surface. 